The Mahr Federal 4487707 844 A Pistol Self Centering Bore Gage Set with 1086 R Digital Indicator is for measuring through holes, blind holes and centering shoulders. This Bore Gage Set features threaded connection for changing the measuring heads, it has Self-Centering measuring head that consists of 3 laterally positioned anvils, each are offset at intervals of 120 degrees. The anvils are carbide tipped and can be used to measure to the bottom of a bore. Supplied with a case and operating instructions. This model has SPC Output and a measuring range of 30-40mm.